Realising voice service

ABSTRACT

A solution for realising voice service comprises connecting to a core network of a cellular network via another wireless network; emulating the operation of a network node by creating a self-serving cell by requesting the core network to establish a cell and by establishing required interfaces between the apparatus and the core network utilising IP Security Architecture (IPSec), and by exchanging signalling with Mobile Management Entity of the cellular network over IPSec tunnel and establishing a voice over cellular network call and transmit voice traffic to Serving Gateway of the cellular network.

TECHNICAL FIELD

The invention relates to communications.

BACKGROUND

In recent years, Instant Messaging (IM) based voice services have beendeveloped to replace or supplement circuit switched voice service. In IMbased voice services voice is transmitted as data. Mobile networkoperators (MNO) which maintain circuit switched services have beenchallenged by over the top (OTT) providers which offer free IM basedservices.

Users expect from IM based voice services similar quality of service asthey have received from circuit switched connections. In solutionspresented so far there has been problems in latency and mobility, forexample.

BRIEF DESCRIPTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is notintended to identify key/critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts of the invention in a simplified form as a prelude to amore detailed description that is presented later.

According to an aspect of the present invention, there is provided anapparatus of claim 1 and an apparatus of claim 9.

According to an aspect of the present invention, there is provided amethod of claim 12 and a method claim 20.

According to an aspect of the present invention, there is provided acomputer program product of claim 23.

According to an aspect of the present invention, there is provided asystem of claim 24.

Some embodiments are described in the dependent claims.

BRIEF DESCRIPTION OF DRAWINGS

One or more examples of implementations are set forth in more detail inthe accompanying drawings and the description below. Other features willbe apparent from the description and drawings, and from the claims.

FIG. 1 illustrates an example of communication environment;

FIG. 2A illustrates a general architecture of an exemplary system;

FIG. 2B is a flowchart illustrating an example embodiment of theoperation of a Radio Access Network Adaptor;

FIG. 3 is a signalling chart illustrating an example of setting up aself-serving cell;

FIG. 4 illustrates an example of user terminal with the RAN Adaptor;

FIG. 5 is a signalling chart illustrating an example of an embodiment;

FIG. 6 is a flowchart illustrating an example of an embodiment ofinitiating a call session;

FIG. 7 is a flowchart illustrating an example of an embodiment ofresponding to an incoming call;

FIG. 8 is a flowchart illustrating an example of a handover;

FIG. 9 illustrates an example of handover connections; and

FIGS. 10 and 11 illustrate simplified examples of apparatuses in whichembodiments of the invention may be applied.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The following embodiments are only examples. Although the specificationmay refer to “an”, “one”, or “some” embodiment(s) in several locations,this does not necessarily mean that each such reference is to the sameembodiment(s), or that the feature only applies to a single embodiment.Single features of different embodiments may also be combined to provideother embodiments. Furthermore, words “comprising” and “including”should be understood as not limiting the described embodiments toconsist of only those features that have been mentioned and suchembodiments may also contain also features, structures, units, modulesetc. that have not been specifically mentioned.

The coverage of cellular service can vary depending on weatherconditions, distance from the serving cell, and obstructions on thesignal path, for example. In some cases indoor coverage may be pooralthough outdoors the coverage is sufficient. This may be due to thestructure of the building and selective glass windows which blockradiation. One solution to improve indoor coverage is to use WirelessLocal Area Network (WLAN, WiFi) as a replacement for cellular coverage.To this end the use of Voice over WiFi has been proposed. VoWiFi is oneway of realizing IM based voice service

FIG. 1 illustrates an example. A user terminal 100 may be connected 102to a cellular network, such as Long Term Evolution (LTE) network or 5Gnetwork, via a network node 104 (may be referred to as a base station104, eNodeB, or a base station apparatus). For example, the network nodemay be connected to Mobility Management Entity/Serving Gateway MME/SGW106 using 51 interface, which may configured to direct the traffic toPacket Domain Gateway PGW 108. MME/SGW may refer to MME or SGW, or insome cases it may refer to both. That is, said MME and SGW may beimplemented as a logically and/or physically integral entity.

The cellular Network may further comprise a Network Management Systementity 110. One example of a cellular network may be the LTE network. Insuch case, the network node may be or be comprised in an evolved NodeB(eNodeB). On the other hand, network node may be a network node of a 5Gnetwork or some other future cellular network. For the purpose ofsimplicity, the following examples are set forth as being part of LTEnetwork. However, it needs to be noted that the solutions and examplesprovided herein may be equally applicable to other types of cellularnetworks, of which the 5G network is one example, although some examplesare described only using LTE and/or eNodeB(s).

The user terminal may also be connected 112 to a wireless local areanetwork access point 114. If a voice over WiFi call is established, itgoes from the access point to a Broadband remote access server BRAS 116of the Internet operator to an enhanced Packet Domain Gateway 118 to theLTE network.

However, there are many problems associated with VoWiFi, such aslatency, when the calls are routed via Internet and when they are routedvia Enhanced Packet Domain Gateway ePDG of the LTE network. BecauseVoWiFi service provider may not control IP backbone or Wi-Fi network,Quality if service (QoS) class identifier cannot be applied in IPbackbone and it may only be performed by ePDG or Trusted Wireless AccessGateway TWAG.

In addition, there are handover related problems. VoWiFi solution can'tsupport handover between trusted Wi-Fi access and untrusted Wi-Fiaccess, because there is no mobility measurement between TWAG and ePDG.Further, different IP addresses are taken into use for WiFi network andLTE RAN, in order to provide connectivity towards core network, whichcause complicated handover mechanism between WiFi network and the LTEnetwork.

Further, similar with regular phone call, a single International MobileSubscriber Identity IMSI (which is stored in Subscriber Identity ModuleSIM hardware) is used for mobile network operator MNO authentication inVoWiFi solution. If the serving MNO ePDG can't be reached via Internetsomehow (e.g BRAS cut down Internet connectivity for marketingcompetition or due to BRAS is owned by another operator), the call pathis broken and there is no alternative way to establish a new callalthough an ePDG of another operator might be available.

FIG. 2A illustrates an example embodiment. To enable making voice callsusing IM based applications especially when cellular (e.g. LTE) coverageis not available, is of poor quality or is lost, the user terminal 100may be configured to communicate with a core network of cellular system(e.g. core network of LTE) via another wireless network such as awireless local area network such as a IEEE 802.11 (WiFi) network byconnecting 200 to the access point 114. IEEE denotes Institute ofElectrical and Electronics Engineers. The user terminal may beconfigured to emulate the operation of a cellular network node of thecellular network (e.g. an eNodeB in the case of LTE) by creating aself-serving cell. The user terminal may request the core network toestablish a cell and by establish required interfaces between the userterminal and the core network utilising IP Security Architecture(IPSec). The user terminal may exchange signalling with MobileManagement Entity of the cellular network over IPSec tunnel andestablish a voice over cellular network call (e.g. voice over LTE) andtransmit voice traffic directly to the Serving Gateway 106 of thecellular network (e.g. the LTE network). That is, the voice overcellular network call may be performed via said another wirelessnetwork. The Serving Gateway 106 may regard such call as a regular voiceover cellular network call although said another wireless network isused as a physical transfer the voice data. In a way, it may beunderstood that the logical connection (e.g. voice over LTE) utilizes aconnection of said another wireless network (e.g. physical connection).The cellular network node may refer to a network node of the cellularnetwork (e.g. eNB).

Thus, for example, the user terminal may be configured to create anon-demand self-serving cell emulating the operation of an eNodeB andcreate a Voice over LTE call using wireless local area networkconnection as a backbone connection. The cell may be created if a userwishes to make a call when there is no LTE coverage or if during anongoing call the LTE coverage is lost or of poor quality but wirelesslocal area network connection is available.

Self-serving cell may be understood as cell that is generated by theuser terminal, wherein the self-serving cell emulates the operation of acellular cell. Thus, it may be seen as a cell of the cellular network byother network elements although it may have been generated by the userterminal using said another wireless network. For example, theself-serving cell may simulate the behavior of a network node (e.g. eNB)of the cellular network.

In an embodiment, the user terminal may comprise a Radio Access NetworkRAN adaptor application which is configured to create the self-servingcell and simulate network node (e.g. eNodeB) behaviour. The RAN adaptormay communicate with the IM client used in IM based voice services, suchas for making IM based voice calls. Thus, the RAN adaptor may hide fromthe IM client the connection type used to create the IM based voicecall. It may be noted that the RAN adaptor cannot service other userterminals since there is no air interface available in the self-servingcell.

In an embodiment, RAN Adaptor may be configured to create theself-serving cell or on-demand cell whenever a connection throughanother wireless network to the LTE Core network can be established.When the actual LTE coverage becomes unavailable, is of poor quality oris lost, a handover to the on-demand cell may be performed without anydropped calls.

FIG. 2B is a flowchart illustrating an example embodiment of theoperation of the RAN Adaptor.

In step 202, the adaptor is configured to connect to a core network of aLong Term Evolution (LTE) cellular network via another wireless network.In this specific example the wireless network, the wireless network is awireless local area network such as according to IEEE 802.11 (WiFi)standard. However, any wireless network offering a connection to an LTENetwork may be used as well. It is yet again noted that the LTE andeNodeB are used as examples. Hence, for example, the steps 202-208 maybe performed in some other type of cellular network (e.g. 5G) by anetwork node of such cellular network.

The RAN Adaptor may be configured to emulate the operation of an eNodeBby

creating in step 204 a self-serving cell by requesting the core networkto establish a cell and by establishing required interfaces between theapparatus and the core network utilising IP Security Architecture(IPSec), and by

exchanging in step 206 signalling with Mobile Management Entity of theLTE network over IPSec tunnel.

In step 208, the adaptor is configured to establish a voice over LTEcall and transmit voice traffic to Serving Gateway of the LTE network.

FIG. 3 is a signaling chart illustrating an example of the creation ofthe self-serving cell. In this example, the user terminal had aconnection to an eNodeB 104 but the connection is transferred to awireless local area network connection.

In advance to the actual cell creation, necessary secure tunnels may becreated to guarantee data security. In phase 300, IPsec Core tunnel iscreated between the SGW 106 and PGW 108. Next, in phase 302, S5/S8interface is created between the SGW and PGW.

In phase 304, user terminal 100 is configured to request MME/SGW IPaddress from PGW 108. The PGW is configured to respond 306 to the userterminal with the MME/SGW IP address.

Next, IPSec radio access network (RAN) is setup 308 between userterminal 100 and SGW 106. IPsec RAN is an IPsec tunnel used forconnecting the self-serving cell with MME/S-GW via BRAS (not shown inFIG. 3).

The user terminal is next configured to request 310 self-serving cell oron-demand cell configuration from the NMS by transmitting a request tothe PGW. The PGW forwards 312 the request to the NMS 110.

The NMS creates on-demand cells on top of the user terminal using cellconfiguration request signalling 314.

The user terminal transmits 316 as a response cell configuration statusto the PGW which forwards 318 the response to the NMS.

Next, the user terminal request 320 S1 interface setup from the MME/SGW106. The MME/SGW responds 322 S1 interface status over IPsec RAN.

In phase 324 the user terminal requests 324 X2 interface setup. Thesetup request is forwarded 326 to the eNodeB by PGW.

The eNodeB responds 328 with X2 status and PGW forwards 330 the X2status to the user terminal.

Finally in this example, the eNodeB requests 332 handover from the userterminal. The PGW forwards 334 the request to the user terminal. Theuser terminal response 336 is sent 338 via the PGW to the eNodeB.

In an embodiment, the request 310 transmitted by the user terminalcomprises an IP address of the user terminal.

In an embodiment, the PGW replaces the IP address of the user terminalin the request with another IP address, before forwarding 312 therequest to the NMS. Alternatively, the PGW may add said another IPaddress to the request. Hence, the forwarded request may comprise bothIP addresses. Said another IP address may be an IP address to be used bythe NMS for responding to the request (e.g. signalling 314). In someembodiments, said another IP address may enable the NMS to respond tothe request. IP address may denote Internet Protocol address. Saidanother IP address may refer to Network-to-Network Interface (NNI) IPaddress used in communication between the NMS and the PGW. The IPaddress may be comprised in the header part of the transmitted request.

In an embodiment, the RAN adaptor may comprise eSIM information of amobile network operator (MNO). An eSIM is an embedded subscriberidentity module in a user terminal. Traditionally, subscriber identityin a user terminal is created with a physical SIM card obtained from aMNO and inserted to a card reader of the user terminal. The SIM containsInternational Mobile Subscriber Identity IMSI of the subscriber. Insteadof a physical card, an eSIM is an embedded chip in the user terminal andit is non-replaceable.

In an embodiment, the RAN Adaptor may comprise more than one eSIMs withmultiple subscriber identities. When making a call the IM client may usepreferred eSIM and create a call session.

In an embodiment, the RAN Adaptor is configured to simulate eNodeBbehaviour including NAS (Non-access stratum) layer, GTP-U (GeneralPacket Radio Service Tunneling Protocol) and Stream Control TransmissionProtocol (SCTP) encapsulation and decapsulation.

In an embodiment, the RAN adaptor may be controlled and managed by MNONMS, and each MNO may own its RAN adaptor.

FIG. 4 illustrates an example of user terminal with a RAN Adaptorinstalled. The figure illustrates an example of the relevant userterminal modules and how the RAN Adaptor may communicate with the IMclient and provide VoLTE call service.

The subscriber or user interacts with the user terminal using an instantmessaging client (IM client) 400 which may be used to initiate andrespond to voice calls. Typically the IM client 400, being anapplication executed by the processor of the user terminal, interactswith the user terminal via an Application Programming Interface 402 ofthe user terminal. In case of voice calls, voice data is sent to a voicecodec 404 which transforms voice into a digital form using suitablecoding.

The user terminal comprises a RAN Adaptor 406, which may also berealised with an application. In an embodiment, the adaptorimplementation comprises following components: An eSIM and CellController 408 is configured to store SIM information andcreate/maintain MNO cell information. A NAS entity 410 is configured tosimulate eNodeB behaviour for NAS signalling handling. The RAN Adaptorcomprises an SCTP encapsulation/decapsulation unit 414 for NASsignalling transport format translation and IPSecencapsulation/decapsulation. The RAN Adaptor further comprises a GTP-Uencapsulation/decapsulation unit 412 for voice data transport formattranslation and IPSec encapsulation/decapsulation. In an embodiment, thecomponents or units may be realised with software or a combination ofsoftware and hardware.

When the IM client is used to make a voice call through LTE RAN, thevoice signal from the IM client may be translated to voice data in thevoice codec 404 and transmitted through the high speed inter-chipcommunication link to LTE base band chip 418 and then sent out via LTEradio frequency unit 420 and antenna 422 to the eNodeB 104.

When using the RAN Adaptor installation, the application is configuredto provide an eNodeB functionality for voice calls. The Adaptor takesover the voice data processing before sending the data to WiFi base bandchip.

FIG. 5 illustrates an example of the operation of the RAN Adaptor. TheIM client 400 is not aware of the way the call is realised. The CellController 408 of the RAN Adaptor simulates the LTE air interfacetowards the application programming interface API 402 and voice codec404. The RAN Adaptor is further configured to translate IM client datainto 3GPP Packet Data Convergence Protocol PDCP format, by simulating3GPP standardized user terminal Medium Access Control 500 and PhysicalLayer 502 protocols. Further, base station Physical Layer 504 and MediumAccess Control 506 simulators are implemented in the GTP-Uencapsulation/decapsulation unit 412 and SCTPencapsulation/decapsulation unit 414 of the RAN Adaptor and they deliver3GPP GTP-U packets to the SGW 106.

FIG. 6 is a flowchart illustrating an example when making a voice callusing the RAN Adaptor.

When an IM client user wants to create a voice call, he may first selectthe installed adaptor application and indicate that a voice call is tobe made. The Adaptor receives 600 the indication and initiates thecalling procedure by providing 602 the user a phone number selection tochoose from. In this example it is assumed that more than one eSIMsubscriber numbers have been installed. If this is not the case, thisstep is skipped. The Adaptor is configured to receive the user selectionand the NAS entity of the Adaptor is configured to initialize signalling604 for VoLTE session setup. In addition, signalling exchange betweenAdaptor and MME is carried over SCTP IPSec tunnel.

After VoLTE session is created, the voice codec is configured togenerate voice data and send to the Adaptor which encapsulates the voicedata with GTP-U over IPSec format and forwards 606 it to Wi-Fi base bandchip. Likewise, the received voice data is forward from the RAN Adaptorto voice codec.

When the IM client user decides 608 to end up the VoLTE call session,the NAS entity of the Adaptor initiates signalling processing 610 forreleasing VoLTE call session. Signalling exchange path is same as instep 604.

As IPSec is created and used for connecting the RAN Adaptor to SGW/MMEso that Quality of Service class identifier QCI can be applied. Comparedto VoWiFi solution, voice traffic latency of the proposed solution isdown from about 150 ms to few milliseconds.

FIG. 7 is a flowchart illustrating an example when receiving a voicecall using the RAN Adaptor.

In step 700, the RAN Adaptor detects incoming call. If the RAN Adaptorcomprises more than one eSIMs and subscriber identities, the Adaptor isconfigured to determine to which identity or phone number the call isdirected to. That is, each of one or more embedded subscriber modulesmay be associated with a different phone number as alternatives forcalling. In step 702, the RAN Adaptor is configured to inform the IMclient about the call, the calling and the called number.

In step 704, the RAN Adaptor is configured to receive call acceptancefrom the IM client.

In step 706, the NAS entity of the Adaptor is configured to initializesignalling for VoLTE session setup. In addition, signalling exchangebetween Adaptor and MME is carried over SCTP IPSec tunnel.

After VoLTE session is created, the voice codec is configured togenerate voice data and send to the Adaptor which encapsulates the voicedata with GTP-U over IPSec format and forwards 708 it to Wi-Fi base bandchip. Likewise, the received voice data is forward from the RAN Adaptorto the voice codec.

When the IM client user decides 710 to end up the VoLTE call session,the NAS entity of the Adaptor initiates signalling processing 712 forreleasing VoLTE call session. Signalling exchange path is same as instep 706.

FIG. 8 is a flowchart illustrating an example of a handover from LTE toRAN Adaptor controlled wireless local area net call.

In step 800, the RAN adaptor determines whether a wireless connection isavailable and a data connection via the connection can be made. Thewireless connection may be via an IEEE 802.11 wireless local areanetwork, for example.

In such a case, the RAN Adaptor is configured to create a self-servingcell in step 802 as described earlier.

In step 804, it is detected that there is a LTE radio connection failureor the LTE quality is degrading.

In step 806, user terminal is configured to perform an inter-cellhandover from the LTE cell to the self-serving cell of the RAN Adaptor.

In the case when there is a voice call connection via the WiFiconnection, and a handover is needed, the RAN adaptor may perform anIEEE 802.11 type handover to another WIFi network for the backbone WiFiconnection. This handover as such does not affect the self-serving cell.Another possibility is to perform an inter-cell handover from theself-serving cell of the RAN Adaptor to a LTE cell, if such isavailable. For example, said cell may be served by the eNB (or ingeneral the cell is served by a network node).

FIG. 9 illustrates an example of handover connections. When the userterminal 100 is connected to PGW via LTE network, there is a radioconnection 102 to the eNodeB 104, from which there is a GTP tunnel 900to SGW 106A and a GTP tunnel 902 to PGW.

When the user terminal 100 is connected to PGW via WiFi network, RANAdaptor in the user terminal has created a GTP connection 904 from theRAN Adaptor to the SGW 106B via the backbone network provided by theWiFi access point 114. The SGW 106B is connected to the PGW via a GTPtunnel 906. The SGWs 106A and 106B may be the same.

Embodiments of the invention, thus utilise a WiFi connection as abackhauling connection. Thus whether the underlying WIFi connection is atrusted or an untrusted Wi-Fi network is of no consequence. The IEEE802.11 standards group provide handover mechanics (between Wi-Fi AccessPoints) for backhauling connectivity. The embodiments provide a 3GPPstandardized inter-cell handover mechanism to support VoLTE callcontinuity across between LTE and Wi-Fi networks, considering voicetraffic is carried via GTP over an IPSec tunnel and reach the SGWdirectly instead of ePDG while the user terminal is attached to theWi-Fi network. Compared to a VoWiFi solution, the proposed solution thecomplicated inter-RAT handover mechanism is much more simplified (asreplaced with an inter-cell handover) and implementation effort is muchsmaller.

The RAN Adaptor may be realised with an application provided by a MobileNetwork Operator MNO. The Application may contain multiple eSIMs.Further, the user terminal may download and install multiple RAN adaptorapplications from more than one MNOs. Thus the user may reach multipleMNO serving access networks. Compared to a VoWiFi solution, over-the-topIM client may select any MNO's RAN to create a VoLTE call sessiondepending on network connectivity and charging costs.

The user terminal (or user equipment, UE) 100 illustrates one type of anapparatus to which resources on the air interface are allocated andassigned, and thus any feature described herein with user apparatus(user equipment) may be implemented with a corresponding apparatus. Theuser apparatus 100 refers to a portable computing device that includeswireless mobile communication devices, including, but not limited to,the following types of devices: mobile phone, smart-phone, personaldigital assistant (PDA), laptop computer, e-reading device, and tablet.

FIG. 10 illustrates an embodiment. The figure illustrates a simplifiedexample of user terminal 100 in which embodiments of the invention maybe applied. It should be understood that the apparatus is depictedherein as an example illustrating some embodiments. It is apparent to aperson skilled in the art that the apparatus may also comprise otherfunctions and/or structures and not all described functions andstructures are required. Although the apparatus has been depicted as oneentity, different modules and memory may be implemented in one or morephysical or logical entities.

The apparatus of the example includes a control circuitry 1000configured to control at least part of the operation of the apparatus.

The apparatus may comprise a memory 1002 for storing data. Furthermorethe memory may store software 1004 executable by the control circuitry1000. The memory may be integrated in the control circuitry.

The apparatus comprises a transceiver 1006. The transceiver isoperationally connected to the control circuitry 1000. It may beconnected to an antenna arrangement 1008 comprising one more antennaelements or antennas. The transceiver may provide the apparatus a radioconnection to a cellular network such as an LTE network. The software1004 may comprise a computer program comprising program code meansadapted to cause the control circuitry 1000 of the apparatus to controlthe transceiver 1006.

The apparatus may comprise another transceiver 1010. The transceiver isoperationally connected to the control circuitry 1000. It may beconnected to an antenna arrangement 1012 comprising one more antennaelements or antennas. The transceiver may provide the apparatus a radioconnection to a wireless local area network, operating according to IEEE802.11 standard. The software 1004 may comprise a computer programcomprising program code means adapted to cause the control circuitry1000 of the apparatus to control the transceiver 1010.

The apparatus may further comprise an interface 1014 operationallyconnected to the control circuitry 1000. The interface may comprise a(touch sensitive) display, a speaker, a microphone, for example.

The control circuitry 1000 is configured to execute one or moreapplications. The applications may be stored in the memory 1002. In anembodiment, the RAN Adaptor described above may be realised as anapplication executed by the control circuitry. Other realisations of theRAN Adaptor, such as hardware or a combination of hardware and softwareare naturally possible as well, as one skilled in the art is aware.

FIG. 11 illustrates an embodiment. The figure illustrates a simplifiedexample of an apparatus acting as a Packet Domain Gateway 108 of an LTENetwork. It should be understood that the apparatus is depicted hereinas an example illustrating some embodiments. It is apparent to a personskilled in the art that the apparatus may also comprise other functionsand/or structures and not all described functions and structures arerequired. Although the apparatus has been depicted as one entity,different modules and memory may be implemented in one or more physicalor logical entities. For example, the apparatus may be realises as oneor more servers connected with each other via Internet.

The apparatus of the example includes a control circuitry 1100configured to control at least part of the operation of the apparatus.

The apparatus may comprise a memory 1102 for storing data. Furthermorethe memory may store software 1104 executable by the control circuitry1100. The memory may be integrated in the control circuitry. The controlcircuitry 1100 is configured to execute one or more applications. Theapplications may be stored in the memory 1102.

The apparatus comprises an interface 1106. The interface isoperationally connected to the control circuitry 1100. It may connectedthe apparatus to other apparatuses or servers of the LTE Network, Thesoftware 1104 may comprise a computer program comprising program codemeans adapted to cause the control circuitry 1100 of the apparatus tocontrol the interface 1106.

The steps and related functions described in the above and attachedfigures are in no absolute chronological order, and some of the stepsmay be performed simultaneously or in an order differing from the givenone. Other functions can also be executed between the steps or withinthe steps. Some of the steps can also be left out or replaced with acorresponding step.

The apparatuses or controllers able to perform the above-described stepsmay be implemented as an electronic digital computer, or a circuitrywhich may comprise a working memory (RAM), a central processing unit(CPU), and a system clock. The CPU may comprise a set of registers, anarithmetic logic unit, and a controller. The controller or the circuitryis controlled by a sequence of program instructions transferred to theCPU from the RAM. The controller may contain a number ofmicroinstructions for basic operations. The implementation ofmicroinstructions may vary depending on the CPU design. The programinstructions may be coded by a programming language, which may be ahigh-level programming language, such as C, Java, etc., or a low-levelprogramming language, such as a machine language, or an assembler. Theelectronic digital computer may also have an operating system, which mayprovide system services to a computer program written with the programinstructions.

As used in this application, the term ‘circuitry’ refers to all of thefollowing: (a) hardware-only circuit implementations, such asimplementations in only analog and/or digital circuitry, and (b)combinations of circuits and software (and/or firmware), such as (asapplicable): (i) a combination of processor(s) or (ii) portions ofprocessor(s)/software including digital signal processor(s), software,and memory(ies) that work together to cause an apparatus to performvarious functions, and (c) circuits, such as a microprocessor(s) or aportion of a microprocessor(s), that require software or firmware foroperation, even if the software or firmware is not physically present.

This definition of ‘circuitry’ applies to all uses of this term in thisapplication. As a further example, as used in this application, the term‘circuitry’ would also cover an implementation of merely a processor (ormultiple processors) or a portion of a processor and its (or their)accompanying software and/or firmware. The term ‘circuitry’ would alsocover, for example and if applicable to the particular element, abaseband integrated circuit or applications processor integrated circuitfor a mobile phone or a similar integrated circuit in a server, acellular network device, or another network device.

An embodiment provides a computer program embodied on a distributionmedium, comprising program instructions which, when loaded into anelectronic apparatus, are configured to control the apparatus to executethe embodiments described above.

The computer program may be in source code form, object code form, or insome intermediate form, and it may be stored in some sort of carrier,which may be any entity or device capable of carrying the program. Suchcarriers include a record medium, computer memory, read-only memory, anda software distribution package, for example. Depending on theprocessing power needed, the computer program may be executed in asingle electronic digital computer or it may be distributed amongst anumber of computers.

The apparatus may also be implemented as one or more integratedcircuits, such as application-specific integrated circuits ASIC. Otherhardware embodiments are also feasible, such as a circuit built ofseparate logic components. A hybrid of these different implementationsis also feasible. When selecting the method of implementation, a personskilled in the art will consider the requirements set for the size andpower consumption of the apparatus, the necessary processing capacity,production costs, and production volumes, for example.

In an embodiment, the apparatus comprises means for communicating with acore network of a cellular system (e.g. LTE) via another wirelessnetwork; means for emulating the operation of a cellular network node(e.g. an eNodeB) by creating a self-serving cell by requesting the corenetwork to establish a cell and by establishing required interfacesbetween the apparatus and the core network utilising IP SecurityArchitecture (IPSec), and by exchanging signalling with MobileManagement Entity of the cellular network (e.g. LTE network) over IPSectunnel; and means for establish a voice over cellular network call (e.g.voice over LTE call) and transmit voice traffic to Serving Gateway ofthe cellular network (e.g. LTE network).

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The invention and its embodiments are not limited to the examplesdescribed above but may vary within the scope of the claims.

1.-24. (canceled)
 25. A user terminal apparatus, comprising: at leastone processor; and at least one memory including a computer programcode, wherein the at least one memory and the computer program code areconfigured, with the at least one processor, to cause the apparatus toperform operations comprising: connecting to a core network of acellular network via another wireless network; emulating the operationof a cellular network node by creating a self-serving cell by requestingthe core network to establish a cell and by establishing requiredinterfaces between the apparatus and the core network utilizing internetprotocol security architecture (IPSec), and by exchanging signallingwith a mobile management entity of the cellular network over an IPSectunnel; and establishing a voice over cellular network call via saidanother wireless network and transmit voice traffic to a serving gatewayof the cellular network.
 26. The apparatus of claim 25, wherein the atleast one memory and the computer program code are configured to, withthe at least one processor, cause the apparatus further to store, in thememory, one or more embedded subscriber modules each with a differentphone number as alternatives for calling or called numbers.
 27. Theapparatus of claim 25, wherein the at least one memory and the computerprogram code are configured to, with the at least one processor, causethe apparatus further to determine that a cell served by a network nodeof the cellular network is available for a voice call; and perform aninter-cell handover from the self-serving cell to the cell served by thenetwork node.
 28. The apparatus of claim 25, wherein the at least onememory and the computer program code are configured to, with the atleast one processor, cause the apparatus further to determine that aconnection to a cell served by a network node of the cellular network islost; create the self-serving cell as a response to the determination;and perform an inter-cell handover from the cell served by the networknode to the self-serving cell.
 29. The apparatus of claim 25, whereinthe at least one memory and the computer program code are configured to,with the at least one processor, cause the apparatus further toestablish an IPSec tunnel between the apparatus and the serving gatewayof a cellular network utilizing wireless local area network as abackhaul connection.
 30. The apparatus of claim 25, wherein the wirelessnetwork comprises an IEEE 802.11 network and the cellular networkcomprises one of a long term evolution cellular network, a long termevolution advanced cellular network, and a 5G cellular network.
 31. Anapparatus, comprising: at least one processor; and at least one memoryincluding a computer program code, wherein the at least one memory andthe computer program code are configured, with the at least oneprocessor, to cause the apparatus to perform operations comprising: actas packet domain gateway of a cellular network; receive a request from auser terminal regarding the internet protocol address of a mobilitymanagement entity or a serving gateway of the network; and transmit theaddress to the user terminal.
 32. The apparatus of claim 31, wherein theat least one memory and the computer program code are configured to,with the at least one processor, cause the apparatus further to receivefrom the user terminal a request for a self-serving cell configuration,the request being directed to the network management system of thecellular network; and transmit the request to the network managementsystem of the cellular network.
 33. The apparatus of claim 32, whereinthe request from the user terminal comprises an internet protocoladdress of the user terminal, the at least one memory and the computerprogram code configured to, with the at least one processor, cause theapparatus further to, before transmitting the request to the networkmanagement system, replace the internet protocol address of the userterminal in the request with another internet protocol address to beused by the network management system for responding to the request, oradding said another internet protocol address to the request.
 34. Amethod in a user terminal apparatus, said method comprising: connectingto a core network of a cellular network via another wireless network;emulating the operation of a cellular network node by creating aself-serving cell by requesting the core network to establish a cell andby establishing required interfaces between the apparatus and the corenetwork utilising internet protocol security architecture (IPSec), andby exchanging signalling with mobile management entity of the cellularnetwork over an IPSec tunnel; and establishing a voice over cellularnetwork call via said another wireless network and transmit voicetraffic to serving gateway of the cellular network.
 35. The method ofclaim 34, further comprising: storing in the memory one or more embeddedsubscriber modules each with a different phone number as alternativesfor calling or called numbers.
 36. The method of claim 34, furthercomprising: determining that a cell served by a network node of thecellular network is available for a voice call; and performing aninter-cell handover from the self-serving cell to the cell served by thenetwork node.
 37. The method of claim 34, further comprising:determining that a connection to a cell served by a network node of thecellular network is lost; creating the self-serving cell as a responseto the determination; and performing an inter-cell handover from thecell served by the network node to the self-serving cell.
 38. The methodof claim 34, further comprising: establishing an IPSec tunnel betweenthe apparatus and serving gateway of a cellular network.
 39. The methodof claim 34, wherein the wireless network comprises an IEEE 802.11network and the cellular network is one of a long term evolutioncellular network, a long term evolution advanced cellular network, and a5G cellular network.
 40. A method in a packet domain gateway of acellular network, comprising: receiving a request from a user terminalregarding the internet protocol address of a mobility management entityor a serving gateway of the network; and transmitting the address to theuser terminal.
 41. The method of claim 40, further comprising receivingfrom the user terminal a request for a self-serving cell configuration,the request being directed to the network management system of thecellular network, transmitting the request to the network managementsystem of the cellular network.
 42. The method of claim 41, wherein therequest from the user terminal comprises an internet protocol address ofthe user terminal, the method further comprising, before transmittingthe request to the network management system, replacing the internetprotocol address of the user terminal in the request with anotherinternet protocol address to be used by the network management systemfor responding to the request, or adding said another internet protocoladdress to the request.
 43. A computer program product embodied on anon-transitory distribution medium readable by a computer and comprisingprogram instructions which, when loaded into an apparatus, execute thesteps of connecting to a core network of a cellular network via anotherwireless network; emulating the operation of a cellular network node bycreating a self-serving cell by requesting the core network to establisha cell and by establishing required interfaces between the apparatus andthe core network utilising internet protocol security architecture(IPSec), and by exchanging signalling with mobile management entity ofthe cellular network over IPSec tunnel; and establishing a voice overcellular network call via said another wireless network and transmitvoice traffic to serving gateway of the cellular network.
 44. A computerprogram product embodied on a non-transitory distribution mediumreadable by a computer and comprising program instructions which, whenloaded into an apparatus, execute the steps of receiving a request froma user terminal regarding the internet protocol address of a mobilitymanagement entity or a serving gateway of the network; and transmittingthe address to the user terminal.